1. Field of the Invention
The present invention relates to a coil-spring manufacturing apparatus which manufactures a coil spring by bending a coil wire material with at least three rolls and by simultaneously applying a pitch to the material with a pitch tool.
2. Description of the Related Art
A coil-spring manufacturing machine using rolls is configured, as described in Jpn. Pat. Appln. KOKAI Publication No. 57-25233, in a manner that two shaping rolls are provided along a conveying direction of a coil wire material on one side of the conveying direction and that a supporting roll is positioned so as to face the two shaping rolls between the two shaping rolls, on the other side of the conveying direction. That is, with reference to the conveying direction of the coil wire material, the two shaping rolls and the one supporting roll are provided respectively on one side and the other side. The supporting roll is movable in up and down directions. The two shaping rolls are arranged bilaterally symmetrical about the supporting roll as a center, and the two shaping rolls are also bilaterally symmetrically movable. Further, a pitch tool which can be moved back and forth along a screwing direction is provided in a lower part of each of these rolls.
The coil-spring manufacturing machine manufactures a coil spring having an arbitrary outer diameter and an arbitrary pitch in a manner that: a spring outer diameter of a coil spring to shape is set by an interval between the two shaping rolls and an increase amount of the supporting roll; a coil wire material is made penetrate among three rolls, positions of which are properly set, to thereby bend and shape the coil wire material; and the bent coil wire material is properly pressed in a screwing direction of the coil spring by the pitch tool, to thereby shape a predetermined pitch.
Recently, a coil spring having a great pitch change is demanded. For example, to manufacture a coil spring which has an increased pitch at a center part in an axis direction of the coil spring, the coil spring is shaped to have a small pitch at the start of winding, which is then increased. At a position beyond a part having the greatest pitch, the pitch needs to be decreased again.